Quoting darkroast (Thread starter):Any reason why this particular flight could be delayed so consistently? Is it because it is one of the very late departures and the delays are cascading?

Only 2 of AC's 5 departures from FRA on Tuesday appear to have operated (YOW and one YYZ flight), and they were both 5 or 6 hours late due to snow that closed FRA airport for much of the day resulting in cancellation of dozens of flights.. The other 3 flights to YYZ/YUL/YYC were cancelled. Monday night's YYC-FRA A333 (AC844) diverted to AMS and appears to be spending the night before continuing to FRA Wednesday morning.

Re AC876 delays, looking at the Flightradar24 site, it appears the 77W that operates AC876 YYZ-FRA is usually the aircraft that operates AC032 PEK-YYZ with a scheduled ground time at YYZ of 3:45.